Bob Nystrom
14011f47e3
They're back from the grave, and ready to party! Change-Id: I088134a9be7ecabf1fbf751c015a656a15cabff9 Reviewed-on: https://dart-review.googlesource.com/12821 Commit-Queue: Bob Nystrom <rnystrom@google.com> Reviewed-by: William Hesse <whesse@google.com>
93 lines
2.2 KiB
Dart
93 lines
2.2 KiB
Dart
// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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import "package:expect/expect.dart";
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// Dart test for deeply nested generic types.
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/** A natural number aka Peano number. */
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abstract class N {
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N add1();
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N sub1();
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}
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/** Zero element. */
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class Z implements N {
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Z();
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N add1() {
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return new S<Z>(this);
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}
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N sub1() {
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throw "Error: sub1(0)";
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}
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}
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/** Successor element. */
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class S<K> implements N {
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N before;
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S(this.before);
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N add1() {
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return new S<S<K>>(this);
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}
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N sub1() {
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// It would be super cool if this could be "new K()".
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return before;
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}
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}
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N NFromInt(int x) {
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if (x == 0)
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return new Z();
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else
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return NFromInt(x - 1).add1();
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}
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int IntFromN(N x) {
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if (x is Z) return 0;
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if (x is S) return IntFromN(x.sub1()) + 1;
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throw "Error";
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}
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bool IsEven(N x) {
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if (x is Z) return true;
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if (x is S<Z>) return false;
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if (x is S<S>) return IsEven(x.sub1().sub1());
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throw "Error in IsEven";
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}
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main() {
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Expect.isTrue(NFromInt(0) is Z);
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Expect.isTrue(NFromInt(1) is S<Z>);
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Expect.isTrue(NFromInt(2) is S<S<Z>>);
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Expect.isTrue(NFromInt(3) is S<S<S<Z>>>);
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Expect.isTrue(NFromInt(10) is S<S<S<S<S<S<S<S<S<S<Z>>>>>>>>>>);
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// Negative tests.
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Expect.isTrue(NFromInt(0) is! S);
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Expect.isTrue(NFromInt(1) is! Z);
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Expect.isTrue(NFromInt(1) is! S<S>);
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Expect.isTrue(NFromInt(2) is! Z);
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Expect.isTrue(NFromInt(2) is! S<Z>);
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Expect.isTrue(NFromInt(2) is! S<S<S>>);
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// Greater-than tests
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Expect.isTrue(NFromInt(4) is S<S>); // 4 >= 2
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Expect.isTrue(NFromInt(4) is S<S<S>>); // 4 >= 3
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Expect.isTrue(NFromInt(4) is S<S<S<S>>>); // 4 >= 4
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Expect.isTrue(NFromInt(4) is! S<S<S<S<S>>>>); // 4 < 5
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Expect.isTrue(IsEven(NFromInt(0)));
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Expect.isFalse(IsEven(NFromInt(1)));
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Expect.isTrue(IsEven(NFromInt(2)));
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Expect.isFalse(IsEven(NFromInt(3)));
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Expect.isTrue(IsEven(NFromInt(4)));
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Expect.equals(0, IntFromN(NFromInt(0)));
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Expect.equals(1, IntFromN(NFromInt(1)));
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Expect.equals(2, IntFromN(NFromInt(2)));
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Expect.equals(50, IntFromN(NFromInt(50)));
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}
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